Think how many fish have been caught over the years by trolling crank baits in 100 feet or more of water. Yes, grinding the bottom is the percentage play and it's pretty much the only way I fish a crank bait these days. But it's not the only way a fish ever bites one. It's just that there are probably better options for swimming a lure these days than in the old days, i.e. swim baits, the modern curly tail grub, suspending jerk baits, underspins, etc.